1. Field of the Invention
The present invention relates to a hydraulic transmission apparatus, and more particularly to a hydraulic transmission apparatus for transmitting power from a power source such as an engine or an electric motor to drive wheels in a self-propelled working vehicle such as a lawn mower of the riding type or walk-behind type, a rotary tiller, a tractor, or the like.
2. Description of the Relevant Art
There have been proposed in recent years self-propelled working vehicles such as a lawn mower of the riding type or walk-behind type, a rotary tiller, a tractor, and the like. In the proposed self-propelled working vehicles, power from an engine or an electric motor is transmitted to drive wheels through a hydraulic transmission apparatus comprising an oil pump, an oil motor, a speed reducer, and other components.
Such a hydraulic transmission apparatus is disclosed in Japanese Pat. Publication No. 50-33283 published Oct. 29, 1975, entitled "Hydraulically driven transmission apparatus for tractors", and Japanese Laid-Open Utility Model Publication No. 60-89454 published June 19, 1985, entitled "Fluid transmission apparatus".
The transmission apparatus disclosed in the former publication has input means to which power is applied from a power source in a prescribed direction and direction changing means for extracting power in a direction different from the prescribed direction. Specifically, a power input shaft extends perpendicularly to a rear wheel axle, and the direction changing means comprises a plurality of bevel gears. Therefore, the transmission apparatus is made up of a large number of parts. As a result, the transmission apparatus is large in size and complex in structure, the process of assembling the transmission apparatus is complicated, and hence the cost of manufacture is high. These problems are amplified by the fact that a speed reducer mechanism is housed in a reducer case, and an oil pump and an oil motor are accommodated in a case separate from the reducer case.
According to the transmission apparatus disclosed in the latter publication, an oil pump and an oil motor are connected to each other by a closed hydraulic circuit. Where the transmission apparatus of this type is incorporated in a working vehicle, a clutch must be disposed between the oil pump and a power source in order to stop rotation of drive wheels for better maneuverability of the vehicle. This results in the same disadvantages as those of the transmission apparatus of the former publication.
U.S. Pat. No. 4,212,141 patented July 15, 1980 which was filed by the applicant discloses a self-propelled lawn mower having an operating device comprising a clutch for selectively rotating and stopping grass cutting blades and a clutch for selectively rotating and stopping drive wheels. First and second levers for operating the clutches are mounted on a handle. The clutches are connected when the levers are moved toward the handle. The first lever is independently movable, whereas when the second lever is moved, it engages the first lever to forcibly move the first lever.
The present invention is directed toward an improvement over the hydraulic transmission apparatus of a self-propelled working vehicle such as a lawn mower, and the operating device of the working vehicle. According to the present invention, the lawn mower can be moved while a cutter is being held at rest, allowing the working vehicle to be maneuvered with ease, and the speed of travel of the lawn mower can easily be adjusted with respect to the speed of rotation of the cutter.